1. Field of the Invention
The present invention relates to a system and a method for synchronizing rotation speed and rotation phase among a plurality of disk units for writing and reading information.
2. Description of the Prior Art
The capacity of a digital data storage system has recently been expanding, and demand for improvement in its data processing speed has been growing. To meet this demand, the method in which a plurality of magnetic disk units are connected in parallel to expand storage capacity and to increase processing speed has been proposed.
FIG. 9 is a block diagram showing a prior art storage system disclosed in Japanese Patent No. 1-250128 for example. In the figure, reference numeral 1 represents a host computer, 2 an array controller, and 3 a disk controller. A plurality of disk controllers 3 are connected to the array controller 2. 4 indicates magnetic disk units, each of which is connected to the respective disk controller 3. 5 indicates a master index line over which a master index signal from the array controller 2 is sent and which is connected to the magnetic disk units 4.
The operation of the storage system will be described hereafter. Data is written and read out from the host computer 1 through the array controller 2. Data is split into pieces for distribution to the magnetic disk units 4 to reduce processing time. The disk controller 3 sends data split by the array controller 2 to the disk controller 3 for writing on the magnetic disk units 4. Data read out from the magnetic disk units 4 is synthesized by the array controller 2 for transmission to the host computer 1. A master index signal for synchronizing the rotation of the magnetic disk units 4 is outputted from the array controller 2 to the master index line 5. All of the magnetic disk units 4 refer to this master index 5 for synchronization with one another.
FIG. 10 is a block diagram showing the rotation synchronization control circuit of the conventional storage system. In the figure, reference numeral 6 represents a spindle motor control circuit, 7 a spindle motor, 8 a phase detection circuit, and 9 a rotation speed control circuit. 10 represents a rotation phase control circuit, 11 a speed reference signal generator circuit, and 12 a phase signal input circuit. The magnetic disk units of the conventional storage system have a function to synchronize the rotation phase of the spindle motor with the master index signal referred to by the phase signal input circuit 12. The rotation phase control circuit 10 of each disk unit compares the master index signal referred to by the phase signal input circuit 12 with the phase of the rotation phase signal detected by the phase detection circuit 8 provided in the same disk unit to output instructions on the acceleration or deceleration of the spindle motor 7 to the speed reference signal generator circuit 11. The rotation speed control circuit 9 of each disk unit compares the speed reference signal from the speed reference signal generator circuit 11 with the rotation phase signal detected by the phase detection circuit 8 provided in the same disk unit to output instructions on the acceleration or deceleration of the spindle motor 7 to the spindle motor control circuit 6.